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      <title>SQL语句在 MySQL 中的执行步骤是什么 - 交互式测验</title>
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          <div class="quiz-container">
            <div class="quiz-header">
              <h1>SQL语句在 MySQL 中的执行步骤是什么 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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  {
    "question": "根据文档，在MySQL中，一条SQL语句在被实际执行之前，哪一个阶段负责生成多种可能的执行计划并从中选择成本最低的一个？",
    "options": [
      "语法解析阶段",
      "预处理阶段",
      "查询优化阶段",
      "执行器执行阶段"
    ],
    "correctAnswerIndex": 2,
    "explanation": "查询优化阶段是MySQL的核心部分之一。在此阶段，查询优化器会分析SQL语句，生成多种可行的执行路径（例如，不同的表连接顺序、是否使用索引等），然后通过成本估算选择一个最高效的执行计划，以供后续的执行器使用。",
    "source": "文档中「一、SQL 语句的基本流程」的第5点「查询优化」及「二、各步骤的详细解释」的第3点「查询优化」",
    "hint": "文档中提到一个核心部分，它决定了SQL语句的执行效率，涉及到选择执行计划、索引使用等策略。"
  },
  {
    "question": "在SQL语句的“预处理”阶段，MySQL会执行以下哪项关键操作？",
    "options": [
      "将SQL语句拆分为关键字、表名等词法单元。",
      "检查SQL语句的语法是否符合规范。",
      "验证语句中涉及的表和列是否存在，并进行权限校验。",
      "根据最终的执行计划从存储引擎中读取数据。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "预处理阶段发生在语法解析之后、查询优化之前。它的主要职责是进行语义层面的检查，包括确认SQL语句中引用的数据库对象（如表、列）是真实存在的，并验证当前用户是否具备执行该操作的权限。",
    "source": "文档中「一、SQL 语句的基本流程」的第4点「预处理」",
    "hint": "在正式优化和执行之前，系统需要确认你“谈论”的东西是存在的，并且你有权去操作它。"
  },
  {
    "question": "文档中提到了“查询缓存”这一机制，关于它在MySQL 8.0版本中的状态，以下哪个描述是正确的？",
    "options": [
      "它被极大地增强了，成为性能优化的核心功能。",
      "它仍然存在，但默认被禁用，需要手动开启。",
      "由于在高并发下存在效率问题，该功能已被移除。",
      "它被一种更先进的内存数据库技术所取代。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档明确指出，虽然查询缓存可以加速完全相同的查询，但它在数据频繁更新和高并发的场景下维护成本高，效率不佳。因此，从MySQL 8.0版本开始，官方决定将这个功能移除。",
    "source": "文档中「二、各步骤的详细解释」的第1点「查询缓存检查」",
    "hint": "对于这个曾经的性能加速机制，文档提到了它在现代高并发环境下的一个重要变化。"
  },
  {
    "question": "当查询优化器生成了最优的执行计划后，哪个组件负责具体实施这个计划，与存储引擎交互并获取数据？",
    "options": [
      "执行器 (Executor)",
      "解析器 (Parser)",
      "预处理器 (Preprocessor)",
      "查询缓存 (Query Cache)"
    ],
    "correctAnswerIndex": 0,
    "explanation": "执行器是SQL执行流程的最后实施者。它接收来自查询优化器的执行计划，然后严格按照计划中的步骤进行操作，通过调用存储引擎的接口来读取数据、进行过滤、排序和聚合等，并最终生成结果集。",
    "source": "文档中「二、各步骤的详细解释」的第4点「执行计划与执行器」",
    "hint": "这个组件是整个流程的“实干家”，负责将“蓝图”（执行计划）变为现实。"
  },
  {
    "question": "在“语法解析”阶段，MySQL会进行“词法分析”和“语法分析”。这两者的主要区别是什么？",
    "options": [
      "词法分析负责检查权限，语法分析负责选择索引。",
      "词法分析将SQL语句分解成独立的“词语”（token），而语法分析则检查这些“词语”组合成的“句子”是否合乎语法规则。",
      "词法分析负责重写查询，语法分析负责生成执行计划。",
      "两者没有本质区别，只是同一过程的两个不同叫法。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "词法分析是第一步，它像一个分词器，将整个SQL字符串切分成有意义的最小单元，如关键字（SELECT, FROM）、标识符（表名, 列名）等。紧接着，语法分析会检查这些单元的排列组合是否符合SQL的语法规范，就像检查一句话的主谓宾结构是否正确一样。",
    "source": "文档中「一、SQL 语句的基本流程」的第3点「语法解析」",
    "hint": "可以类比学习一门语言的过程：首先要认识单词（词法），然后才能学习如何将单词组成正确的句子（语法）。"
  },
  {
    "question": "以下哪项任务不属于“查询优化”阶段的工作范畴？",
    "options": [
      "选择使用哪个索引来访问数据。",
      "决定多表连接时的最佳顺序。",
      "将子查询重写为更高效的连接查询。",
      "检查SQL语句中是否存在拼写错误或不符合SQL规范的语法。"
    ],
    "correctAnswerIndex": 3,
    "explanation": "检查SQL语句的拼写和语法规范是“语法解析”阶段的任务。查询优化阶段则是在确保语法正确无误之后，专注于如何以最高效的方式去执行这条语义上已经合法的SQL语句，其工作包括索引选择、连接顺序优化和查询重写等。",
    "source": "文档中「一、SQL 语句的基本流程」的第5点「查询优化」和第3点「语法解析」",
    "hint": "思考一下，在考虑“如何把事情做得更好”之前，我们首先需要确认“要做的事情本身是否正确”。"
  },
  {
    "question": "如果MySQL启用了慢查询日志（slow query log），记录查询信息的操作通常发生在哪个步骤之后？",
    "options": [
      "查询优化之后，执行计划之前",
      "语法解析之后，预处理之前",
      "客户端发送请求时",
      "结果返回给客户端之后"
    ],
    "correctAnswerIndex": 3,
    "explanation": "根据文档描述的流程，查询日志记录是整个SQL执行过程的最后一步。在执行器完成所有操作并将结果集成功返回给客户端后，MySQL会根据配置（如是否启用慢查询日志以及查询执行时间是否超阈值）来决定是否将该查询的相关信息写入日志文件，以供后续分析。",
    "source": "文档中「一、SQL 语句的基本流程」的第8点「查询日志记录」",
    "hint": "日志记录通常是为了事后分析，因此它会在整个事件（SQL执行）完成后进行。"
  }
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            const wrongCount = answeredCount - correctCount;
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            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

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                '<div class="score-summary">' +
                '<div class="score-card">' +
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                '<div class="score-card">' +
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                '<div class="score-card">' +
                '<h3>错误率</h3>' +
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                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  